1. Field of the Invention
The present invention relates to a parallel robot provided with a wrist section having three degrees of freedom.
2. Description of the Related Art
Various types of parallel robots, in which a plurality of actuators (e.g., servo-motors) are attached to a stationary member acting as a base section and links joined to the output parts of the actuators are respectively driven so as to control the position and orientation of a movable section attached to the distal end of each link, have been known in the art. A parallel robot has a configuration in which the base section is connected to a movable section by a plurality of assembled-link structures arranged in parallel, and thereby has characteristics, such as high accuracy, high stiffness, high speed, high output, etc. Because of these characteristics, a parallel robot may be used as a robot for high speed handling or assembling.
FIG. 11 illustrates the parallel robot described in Japanese Examined Patent Publication (kokai) No. 4-45310 (JP4-45310B). The illustrated parallel robot has a configuration referred to as a delta-type, and includes a single base member 200 and a single movable member 208.
The base member 200 is provided with three rotary actuators 213. Each of the rotary actuators 213 includes a single stationary portion 203 formed integrally with the base member 200. The rotary shafts 202 of the three rotary actuators 213 are disposed in an identical plane. Each of three driving links 204 is fixedly attached at one end 215 thereof to each rotary shaft 202. The other end 216 of each driving link 204 is joined to two driven links 205a, 205b through two Cardan-type double joints 206a, 206b. 
The two driven links 205a, 205b in each assembled-link structure are joined to the movable member 208 through two Cardan-type double joints 207a, 207b. As a result, it is possible to control the motion of the movable member 208 while controlling the operation of the driving links 204, so as to allow the movable member 208 to perform a three-axis translational motion. A working member (hereinafter referred to as a tool) such as a hand 209, etc., may be mounted on the movable member 208.
An orientation changing axis (referred to as a fourth axis) 200A for changing the orientation of the tool, such as the hand 209, etc., is set in the movable member 208 so as to extend orthogonally to the major surface of the movable member 208. The tool, such as the hand 209, etc., is driven for rotation through a telescopic arm 214 by a rotary motor 211 mounted on the base member 200. The three actuators 213 and the rotary motor 211 are controlled by a controller 212.
The parallel robot disclosed in JP4-45310B is provided with the orientation changing axis 200A, referred to as the fourth axis, for changing the orientation of the tool, such as the hand 209, etc., disposed on the movable member 208. However, it is difficult to perform a task for mounting a workpiece to an inclined surface only by a single orientation changing axis (i.e., the fourth axis).